1. Field of the Invention
This invention relates to a method of inspecting a floppy disk casing having a liner applied to the inner surface thereof, and more particularly to a method of inspecting application of the liner to the casing.
2. Description of the Prior Art
Generally, a floppy disk is loaded in a recording and reproducing system as it is accommodated in a thin casing made of plastic or the like. Any dust deposited on the disk surface will adhere to the magnetic had, adversely affecting recording and reproduction. Accordingly, a cleaning liner generally made of non-woven fabric obtained by bonding together fibers of rayon, nylon, PET, polypropylene or the like (several tens of micrometers to several hundreds of micrometers in thickness) is applied to the inner surface of the casing to remove dust on the disk as the disk is rotated for recording or reproduction. The casing is for accommodating therein the floppy disk and is generally referred to as a "shell" or "jacket".
The liner must be applied to the inner surface of the casing in a predetermined position, otherwise the cleaning effect of the liner may be lowered or the liner may damage the disk. Accordingly, application of the liner, is inspected during the manufacturing step of the floppy disk, i.e., to check whether the liner is applied to the inner surface of the casing in a satisfactory state.
In accordance with a conventional method of inspection, before the casing halves are connected together, visible light is projected onto each casing half from the liner side and reflected light from the casing half is received by a light receiving means such as an industrial television camera to obtain image signals by way of photoelectric conversion. The intensity distribution of the image signals thus obtained is subjected to threshold processing and whether the liner is applied to the inner surface of the casing in a satisfactory state is determined on the basis of the result of the threshold processing. However, since the difference in light absorption between the liner and the casing is small, especially when the liner and the casing are of similar colors, it is very difficult to determine whether application of the liner is satisfactory without disturbance arising from noise.